Rotary work carrier arrangement for a double disc grinder

ABSTRACT

A work carrier is disclosed in which a pair of carriers are rotatably mounted on either side of a swing arm assembly, each carrier adapted to receive a workpiece which is held therein for grinding by a three-point rest support engaging the reverse side of the workpiece surface to be ground, and by a series of peripheral locaters to accurately position the workpiece while minimizing mechanical distortion incidental to such positioning. Both of the carriers are rotated in such a position that the workpieces remain in continuous contact with the grinding discs during grinding with this rotation being accomplished by a fluid motor and chain drive arrangement, the chain drive being located in internal openings in a member included in the swing arm assembly so as to be totally enclosed and protected from the abrasive grit. The swing arm assembly includes an upper swing arm assembly detachably mounted to a pivot housing adapted to be pivoted about a pivot shaft to swing the carriers into position between the discs. The upper swing arm assembly extends at an angle to the pivot housing so that the rotary drive motor may be located well above the coolant bin, and the detachable mounting allows ready replacement of the swing arm assembly without the necessity of removing the pivot housing. A specific work ejector mechanism is also described consisting of a pair of plungers carried in a central portion of the work carrier and adapted to be axially extended by a power cylinder and ejector mechanism so as to push the workpieces from the work carrier after grinding.

United States Patent [191 Fallon I Apr. 2, 1974 1 ROTARY WORK CARRIER ARRANGEMENT FOR A DOUBLE DISC GRINDER [75] Inventor: Herbert J. Fallon, Beloit, Wis.

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

[22] Filed: June 12, 1972 [21] Appl. No.: 261,890

[52] US. Cl. 51/118, 51/237 R [51] Int. Cl B24b 5/02 [58] Field of Search 51/111R,112,115,118,

51/113,114, 237 R, 124 R, 234, 82, 85 R, 89, 215 UE; 279/1 E Primary Examiner-Al Lawrence Smith Assistant Examiner-Nicholas P. Godici Attorney, Agent, or Firm-John R. Benefiel [57] ABSTRACT A work carrier is disclosed in which a pair of carriers are rotatably mounted on either side of a swing arm assembly, each carrier adapted to receive a workpiece which is held therein for grinding by a three-point rest support engaging the reverse side of the workpiece surface to be ground, and by a series of peripheral 10- caters to accurately position the workpiece while minimizing mechanical distortion incidental to such positioning.

Both of the carriers are rotated in such a position that the workpieces remain in continuous contact with the grinding discs during grinding with this rotation being accomplished by a fluid motor and chain drive arrangement, the chain drive being located in internal openings in a member included in the swing arm assembly so as to be totally enclosed and protected from the abrasive grit.

The swing arm assembly includes an upper swing arm assembly detachably mounted to a pivot housing adapted to be pivoted about a pivot shaft to swing the carriers into position between the discs. The upper swing arm assembly extends at an angle to the pivot housing so that the rotary drive motor may be located well above the coolant bin, and the detachable mounting allows ready replacement of the swing arm assembly without the necessity of removing the pivot housing.

A specific work ejector mechanism is also described consisting of a pair of plungers carried in a central portion of the work carrier and adapted to be axially extended by a power cylinder and ejector mechanism so as to push the workpieces from the work carrier after grinding.

20Clairns, 12 Drawing Figures PATENTEDMR 2 I974 SHEET 3 [1F 7 F'ATENTEU APR 2 i974 SHEET U 0F 7 FIG.4

PATENTEDAPR 21974 sum 5 OF 7 PATENTEU APR 2 I974 sum 5 OF 7 [Hill] I ROTARY WORK CARRIER ARRANGEMENT FOR A DOUBLE DISC GRINDER BACKGROUND OF THE INVENTION 1. FIELD OF THEINVENTION This invention concerns double disc grinders, and more particularly work carriers for double disc grinders.

2. DESCRIPTION OF THE PRIOR ART Surface grinding of workpieces to obtain flatness within reasonably close tolerances has long been done by machines in which the work is reciprocated relative the peripheral surface of a grinding wheel, or in which the work is held on a rotary table or work carrier which is adapted to rotate the workpieces past the radial face of a rotating grinding wheel.

While satisfactory results are obtained for relatively small, solid workpieces, in attempting to grind surfaces of large workpieces having thin-walled portions, deflections of the workpiece which occur as the grinding wheel engages and disengages the workpiece tend to lessen the degree of flatness obtained, so that for such parts having close tolerance requirements, these approaches are not feasible.

In order to overcome this problem alternate grinding processes in which the workpiece is rotated in the grinding zone in continuous contact with the wheel have been previously utilized, but have primarily been limited to single workpiece and/or single grinding disc type arrangements, which of course limits the rate of production.

Also, implementing such an approach with large, thin-walled, aluminum parts leads to difficulties in holding the workpiece during the rotation and grinding, since if the part is clamped, rather large deflections occur which prevent the obtaining of very flat surfaces.

Yet another problem exists in driving and supporting a work carrier in the grinding zone since the abrasive grit will quickly wear out most chains, bearings, etc., if these are allowed to be exposed thereto.

Additionally, in supporting a rotary carrier on a frame for swinging movement into the grinding zone such as described in US. Pat. No. 2,899,779 and French Pat. No. 829,444 the rotary drive has been received from a point low on the frame, which leads to possible problems of interference with the coolant bin, usually located in the same vicinity. Also such designs having one piece or integral arms often require removal of the entire arm and carrier assembly for service and/or repair.

Finally, it would be advantageous to incorporate an ejector mechanism for unloading the workpieces after grinding, but the basic arrangements heretofore used have tended to preclude the use of such mechanisms.

Therefore, it is an object of the present invention to provide a rotary carrier arrangement for rotation of workpieces during grinding operations which carrier arrangement is moveable into the grinding zone so that the workpiece remains continuously in contact with the grinding disc during grinding thereof, and which is capable of supporting a plurality of workpieces without applying significant clamping pressures.

Another object of the present invention is to provide a rotary drive and support arrangement for the carrier which is enclosed so as to be sealed from the abrasive grit. I

A further object is to incorporate a workpiece ejector mechanism into this basic arrangement.

Yet another object of the present invention is to provide a swing arm assembly which allows for a relatively high location of the rotary drive, and also ready removal of the portion of the swing arm which supports the rotary work carrier arrangement.

SUMMARY OF THE INVENTION These and other objects which will become apparent upon a reading of the following specification and drawings is accomplished by an arrangement wherein a pair of axially aligned rotary workholders are rotatably supported on a two-piece swing arm assembly, each workholder adapted to receive a workpiece and support. the same on a three-point workrest combined with a very light peripheral pressure. The swing arm assembly is adapted to move the workholders between the discs of a double disc grinder for rotation during the grinding operation.

Both workholders are rotatably supported and driven by means of drive and bearing components completely enclosed within the swing arm so as to be sealed from the abrasive grit generated during grinding.

An ejector mechanism located centrally of the workholders and including a pair of knockout plungers axially extended by a power cylinder and and ejector plunger to engage the workpieces and eject the same after the grinding operation is performed.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a double disc grinder incorporating a work carrier arrangement according to the present invention.

FIG. 2 is an enlarged perspective view of the work carrier arrangement shown in FIG. 1 from another. angle.

FIG. 3 is a side elevational view of the swing arm assembly in two of its operating positions.

FIG. 4 is a front elevational view of the swing arm assembly shown in FIG. 3.

FIG. 5 is a detailed side elevational view of the upper arm assembly shown with the workpiece and workpiece retainer removed.

FIG. 6 is the partial view taken in the direction of the arrows 6-6 in FIG. 5.

FIG. 7 is a partial section taken along the line 7--7 in FIG. 5.

FIG. 8 is a sectional view takn along the lines 88 in FIG. 5.

FIG. 9 is a view taken in the direction of the arrows 9--9 in FIG. 7.

FIG. 10 is a partial section taken along -the line 10-10 in FIG. 9.

FIG. 11 is an enlarged side elevational view of a portion of the upper swing arm assembly showing the workpiece and workpiece retainer in place.

FIG. 12 is a view of the dressing unit taken in the direction of the arrows 12-12 in FIG. 11.

DETAILED DESCRIPTION In the following detailed description certain specific terminology will be utilized for the sake of clarity and a specific embodiment will be described in order to provide a complete understanding of the invention, but

it is to be understood that the invention is not so limited and may be practiced in a variety of forms and embodiments.

Referring to the drawings and particularly FIGS. 1 and 2, a double disc grinder is depicted therein together with the work carrier arrangement 12 according to the present invention. The double disc grinder which is of conventional design includes a pair of wheel-head assemblies supported in housings l4 and 15 which are adapted to support and rotate a pair of disc grinding wheels 16 (FIG. 2) and 18 within an enclosure 20.

As is well known in the art, the double disc grinder is adapted to rotate and advance the grinding wheels 16 and 18 along the direction of their rotation in order to grind surfaces on the workpieces disposed in the grinding zone consisting of the space 22 between these grinding wheels 16 and 18, by means of engagement with the radial faces thereof. For this purpose conventional drive and feed advance mechanisms as well as automatic cycle controls 24 according to conventional design principles may be used, and for this reason a detailed description is not here included.

The work carrier arrangement 12 according to the present invention includes a swing arm assembly 26 pivotally supported on trunnions 28 and 30 and positioned to swing a pair of workpieces 32, one supported in each of workholders 34 and 36, into the grinding zone 22 so that each of the workpieces 32 is in contact with a respective grinding disc 16 or 18 during grindmg.

The workholders 34 and 36 are supported for rotation on an upper arm assembly 38 and adapted to be rotated by a fluid motor 40 and a drive system to be hereinafter described in detail during the grinding operation, which is carried out by rotation and infeed of the grinding wheels 16 and 18 into engagement with the workpiece 32 after the swing arm assembly 26 has moved the workpieces into the zone 22 and rotation of the workholders 34 and 36 has been initiated.

After grinding, the swing arm assembly 26 is retracted and the workpieces 32 are discharged from the workholders by axial movement of a pair of knockout plungers 42 (FIG. 7) and 44 (shown exposed in FIG. 2 with the workpiece 32 removed) to be received in a pair of a discharge chutes 46 and 48 (shown in FIG. 4 and not shown in FIG. 2 for the purpose of clarity).

These discharge chutes 46 and 48 preferably are lined with a cushioning low-friction material such as tetrafluoroethylene, in order to minimize damage to the workpieces 32 during ejection thereof.

A large coolant bin 50 is included to receive the large volume of coolant-lubricant usually directed into the grinding zone 22 during grinding operations.

Referring to FIGS. 3 and 4, the details of the arrangement for pivoting the swing arm assembly 26 are shown together with a showing in FIG. 3 of the relative position of the arm assembly 26 in the operative and retracted position.

As can be seen in these Figures, the swing arm assembly 26 includes an upper arm assembly 38 and a lower pivot housing 52 detachably connected together along at a mounting surface 54 defined by the upper surface of a plate 56 integral with the pivot housing 52, by means of a pair of angle brackets 58 and 60 bolted to the plate 56 and to an arm member 62 of the upper arm assembly34.

The pivot housing 52 includes a back plate 64 and a pair of side plates 66 and 68 welded together with plate 56. Side plates 66 and 68 are welded to a pair of block members 70 and 72 fixed to pivot shaft 74, in turn rotatably supported in trunnions 28 and 30 including a pair of bearing assemblies 76 and 78 supported on a fixed frame 80, including a pair of fixed side members 82 and 84.

The pivot housing 52 is adapted to be pivoted about the pivot shaft 74 axis by means of a power cylinder 86, the housing 88 of which is pivotally supported at 90 in a fixture pivot bracket 92 supported by web plates 94 and 96 and vertical plates 98 and 100 welded into the frame 80.

The operating rod 102 is pinned at 104 between a pair of webs 106 and 108 welded into the pivot housing 52, so that extension thereof by pressurization of the power cylinder 86 causes a rocking pivoting of the pivot housing 52 about the axis of pivot shaft 74.

FIG. 3 shows the relative position of the swing arm assembly in. the full in position in solid lines, while the load out and max out positions are depicted in phantom lines.

The load out position is used during removal of workpieces 32 and the max out for a grinding disc dressing operation to be hereinafter described.

Control of the position of the pivot housing 32 may be advantageously carried out by a limit switch assembly 110 cooperating with dowel pins 112 emplaced in collars 114 and 116 on extension 118 of the pivot shaft 74 (best seen in FIG. 1) located in the proper angular position for controlling valving (not shown) for the power cylinder 86 pressure source (also not shown).

As can be seen in FIGS. 1 and 2, by virtue of the angularity of the pivot housing 52 relative to the upper arm assembly 38, the rotary fluid motor 40 can be mounted relatively high and remains above the level of the coolant in coolant bin 50 even in the full out position, so that it is not subjected to possible deleterious effects from immersion to coolant therein. Also, the upper arm assembly 38 is readily detachable for service requirements without the need of removing or replacing the relatively massive and costly pivot housing 52.

Referring to FIGS. 5 12, the details of the upper arm assembly 38 are shown, which includes the arm member 62 consisting of a thick elongated preferably aluminum plate detachably fastened to the pivot housing 52 as described above, to extend at an angle to the pivot housing 52.

The pair of workholders 34 and 36 are rotatably mounted on the arm member 62 by means of a central hub 120 disposed within an opening 122 and mounted for rotation by bearings 124 and 126 the inner races 128 and 130 of which are clamped to the central hub 120 by bearing clamps 132 and the outer races 136 and 138 of which are clamped to the arm member 62 by means of bearing clamps 140 and 142 cooperating with bearing pots 144 and 146 to thus rotatably support the central hub 120 in the arm member 62.

Both of the workholders 34 and 36 are fastened to the central hub 120 at opposite axial ends thereof by a series of capscrews 148 passing through face plates 150 and 152 of each workholder 34 and 36 respectively so that the workholders 34 and 36 are likewise rotatably supported in the arm member 62.

The inner surface of each retainer plate and the outer surface of bearing clamps 140 and 142 are formed with complementary series of annular grooves so that labyrinth type seals are created at 154 and 156 to effectively isolate the bore 122 and bearings 136 and 138 from the entrance of coolant and abrasive grit.

In order to rotate the workholders 34 and 36 by means of the fluid motor 40, a chain drive is provided including a drive hub 158 and connected sprocket 160 fastened to the output of the fluid motor, and extending into a bore 158 (FIG. 6) machined into the lower end of the arm member 62 and closed by cover plate 162.

Affixed to the central hub 120 is a second sprocket 164 and drivingly connecting the sprockets is a roller chain 166 passing around each sprocket and a pair of drilled passages 168 and 170 extending through the arm member 62 along the upper and lower line of tangencies between the two sprockets 160 and 164 to provide a complete path for travel of the roller chain 166.

These passages 168 and 170 are made by drilling through counterbores 172 and 174 respectively, and then covering the same with acovcr plate 176. Thus it can be seen that the sprocket drive moving parts are completely enclosed and sealed within the arm member 62 againstthe entrance of abrasive 'grit and other foreign matter to prevent the resulting wear.

In order to provide adjustability of the chain tension, the fluid motor 40 is fastened to a plate 178 in turn mounted to the arm 62 by three capscrews 180, 182, and 184, two of which, 180 and 182, pass through slotted openings 186 and 188 to allow angular adjustment about the third capscrew 184 to thereby adjust the difference between centers of the sprockets 160 and 164. An adjustable stop 190 is also provided to positively maintain any given adjusted position.

Knockout heads 42 and 44 are operated by an ejector mechanism also contained within the arm member 62. This mechanism includes a pair of knockout plungers 192 and 194 fastened to the knockout heads 42 and 44, and slidably disposed in bushings 196 and 198 in turn contained in ejector bushings 200 and 202. Ejector bushings 200 and 202 are fastened to central hub 120 so as to rotate therewith and extend into a central bore 204 formed in central hub 120.

Each of the ejector plungers is formed with cam head portions 206 and 208 including raised shoulders 210 and 212 which are engaged with respective washers 214 and 216 in turn biased into engagement therewith by means of a set of compression springs 218, 220, 222, and 224 (FIGS. 7, 9, causing the ejector plungers 192 to be biased towards the center of the arm member 62 to the position shown in FIG. 7. A similar set (not shown) is provided for ejector plunger 194.

In order to prevent rotation of the ejector plunger 192, roll pins 226 and 228 are provided, engaging the sides of cam head portion 206 (FIG. 10). Similar roll pins (not shown) are provided for ejector plungers 194.

Each cam head portion 206 and 208 is formed with a sloping cam surface 230 and 232 respectively which engage complementary surfaces 234 and 236 formed on an ejector plunger 238 slidably disposed in a bushing 240 in turn disposed in a radially extending bore in central hub member 120. Ejector plunger 238 is also biased to the position shown in FIG. 7 by a compression spring 242 passing through clearance arcs 244 and 246 in cam heads 206 and 208 and seated in pocket 248 in central hub and pocket 250 in the ejector plunger 238.

Ejector plunger 238 is slotted at 252 in order to straddle the sprocket 164, and has an upper Y-shaped portion 254 to accommodate the roller chain 166. Each arm 256 and 258 of Y-shaped portion 254 has a radiused end portion 260 and 262 which are cencentric with the axis of rotation of the central hub 120 for a purpose to be herein described. The ejector plunger 238 is operated by means of a power cylinder 264 secured to arm member 62 and having an operating rod 266 extending into a radial opening in the arm member 62, formed with a clearance passage 268 also designed to straddle the roller chain 166 and sprocket 164 when reciprocated into contact with the ejector plunger 238.

From the description given thus far, it can be appreciated that since the operating rod 266 is relatively stationary and the ejector plunger 238 rotates with the central hub 120, some means for aligning the two must be provided in order for the device to operate.

In this instance, an angular position sensor arrangement is provided consisting of a sensor pickup 270 and a sensor block 272 which at an appropriate time in the cycle (after grinding is complete) senses when the sensor block 272 is in a position and ejector plunger 238 and through appropriate control means (shown as block 273) cause the fluid motor to discontinue rotation of the central hub 120.

Since precision components or expensive supplementary deviceswould be required to produce accurate alignment of these two elements relief cutout 274 is provided in central hub 120 so that when combined with the radiused nature on surfaces 260 and 262 on an arc concentric with the axis of the central hub 120, considerable misalignment of these parts can occur, without a malfunction and without affecting the stroke of ejector plunger 238.

In operation, after the grinding cycle is completed and the swing arm assembly 12 has been retracted to the unload position, the fluid motor discontinues rotation of the central hub alignment of the pickup sensor 270 and 272 which produces at least rough alignment between operating rod 266 andejector plunger 238. At this point, power cylinder 264 is cycled by control 273 causing operating rod 266 to contact surfaces 260 and 262 and force ejector plunger downwardly as viewed in FIG. 7 against the force of bias spring 242, camming knockout plungers outwardly to cause the knockout heads 42 and 44 to contact their respective workpieces 32 forcing them out of the workholders 34 and 36 and into the discharge chutes 46 and 48.

It can be appreciated that the ejector mechanism is also mostly enclosed within the arm member 62, except for the ejector plungers 192 and 194 in their extended position and hence is protected from abrasive grit. The ejector plungers 192 and 194 themselves are protected by a pair of wipers 176.

Each of the workholders 34 and 36 includes face plates and 152 previously mentioned, and a pair of work retrainers 278 and 280 fixed to a respective face plate 150 and 152. By means of a series of capscrews 279, with a series of spacers 287 used to create openings 283 and 285 to allow grit and sludge to pass out. As shown in FIG. 11, each work retainer 278 and 280 is formed with a respective opening 282 and 284 roughly complementary to the workpiece 32 outline so that a series of adjustable straps 286 can be positioned juxtaposed to the workpiece periphery. The adjustable straps 286 are disposed in slots 288 formed in each work retainer 278 and 280 and are adjustably positioned therein by means of capscrews 290 and slotted openings 292 in the adjustable straps, with the adjusted position positively maintained by a series of eccentrically mounted elements 294 adjusted to engage the outer edge of each adjustable strap 286.

Since there may be considerable variation in the outer dimensions of the workpieces 32, each of the adjustable straps is adjusted so as to accept the normal range of workpiece sizes, which means many of the workpieces will be received rather loosely in openings 282 and 284. In order to apply a light pressure sufficient to prevent the workpiece 32 from falling out, a spring loaded plunger 296 is included which engages the workpiece with a light pressure sufficient to retain the workpiece 32 without imposing significant distortion thereof.

The workpiece 32 is positioned in the plane of grinding by three rests 298 engaging the back side of the workpiece 32. These rests 298 consist of bolts having radiused caps which are threaded into steel insert plates 300 fastened to face plates 150 and 152. The steel insert plates 300 are included since it has been found that if the face plates 150 and 152 are made of aluminum they inadequately retain a threaded connection if the rests 298 are threaded directly thereinto.

It has been found that the location of the three rests 298 with respect to the workpiece 32 are critical to obtaining best results. It can be appreciated that inasmuch as three points define a plane, it is essential that the workpiece 32 remain firmly seated on all of the rests 298 throughout the grinding cycle. Accordingly, during rotation of the workpiece 32 any given location of the workpiece 32 at which there is a rest 298 should not pass too far out of engagement with the guiding wheel face, lest tipping should occur. On the other hand, the rests 298 ideally should be located near the outer periphery of the workpiece 32 to minimize the length of overhangs subject to bending as a result of loading imposed by the grinding wheel. Thus an approximate location can be arrived at in balancing these two considerations, but in addition, it has been found that small adjustments in the rest locations significantly effect results. Inasmuch as this situation seems to result from complex patterns of deflections occurring because of interactions of the workpiece 32 and the grinding wheel, it is best to determine the precise best location by trial and error experimentation.

Along these same lines, it has been found that the precise position of the workpiece 32 location in the grinding zone as positioned by the swing arm assembly 12 is critical in obtaining proper results. Primary considerations are to maintain pressure over as wide an area as possible at all times while allowing the workpiece 32 to sweep out past the inner and outer edges 302 and 304 (FIG. 12) to break these edges in accordance with standard grinding practices, and also to do as much grinding as possible with the higher surface speed outer portion of the grinding wheel. However, in similar fashion to the rest locations, minor trial and error adjustments are advantageous in obtaining best results, due to these same complex factors.

This arrangement also may advantageously incorporate a dress 306 unit carried by the swing arm assembly inasmuch as it eliminates an extra swing arm and insures dressing the surfaces perfectly parallel with the plane of rotation of the workholders 34 and 36.

For this purpose a dressing fixture 308 is fastened to the arm member 62 along the edge 310, and a diamond nib holder 312 and 314 adjustably held therein with diamond nibs 316 and 318 in turn held in the holders 312 and 314. The holders are adjusted to dress the grinding wheel to the proper level by suitable gaging set up and then the swing arm assembly is swung from its full out to full in position past the rotating grinding wheels 14 and 15 to renew and true their radial surfaces.

From the above description it can be appreciated that the objects of the invention have been attained by this carrier arrangement 12. Two workpieces at a time are ground with continuous engagement with the grinding wheel 14 and 15 without significant clamping pressure. In connection with this point, it will be appreciated that the peripheral straps 286 and rest 298 resist the grinding loads passively, and do not impose distorting loads in the absences of grinding forces, the effect of these latter forces being taken care of by a suitable spark-out or dwell period in the manner well known in the art.

Furthermore this arrangement has also provided a simple and trouble-free ejector mechanism as well as a completely enclosed rotary drive system for the workholders.

In addition the upper arm assembly 38 allows for ready serviceability as well as a high location for the rotary fluid motor 46.

Therefore, what is claimed is:

1. A double disc grinder of the type having a pair of opposing radial face grinding discs defining a pair of grinding planes and adapted to be rotated and advanced towards each other to carry out grinding of workpieces disposed therebetween, the improvement comprising:

at least two workholder means, each adapted to hold a workpiece such that a single planar surface of said workpiece can be ground;

arm means rotatably supporting one of said at least two workholder means on either side of said arm means;

means rotating said at least two workholder means on said arm means during grinding of said workpieces;

means positioning said arm means between said grinding discs so that each of said workpieces held and rotated by said workholder. means remain in continuous contact with only one of said grinding discs during said rotation of said workholders and grinding by said grinding discs.

2. The double disc grinder according to claim 1 wherein said workholder means includes a three-point support adapted to engage the workpiece on the side of said workpiece opposite to the surface ground so as to locate the workpiece surface to be ground in the plane of grinding.

3. The double disc grinder of claim 2 wherein said workholder means includes a series of locator points extending about the periphery of said work-piece to position said workpiece laterally during grinding.

4. The double disc grinder of claim 3 further including a member resiliently biased into engagement with said workpiece periphery exerting a retention pressure thereon.

5. The double disc grinder according to claim 1 wherein said means positioning said arm means includes means pivotally supporting said arm means for movement between said discs.

6. The double disc grinder of claim 5 wherein said arm means includes a pivot housing extending from said pivotal support and further includes an upper arm assembly rotatably supporting said workholders, and also including means mounting said upper arm assembly at an angle to said pivot housing.

7. The double disc grinder of claim 6 wherein said means mounting said upper arm assembly includes a detachable connection therebetween.

8. The double disc grinder of claim 3 wherein said means positioning said arm means includes means pivotally supporting said arm means for movement between said discs.

9. The double disc grinder of claim 8 wherein said gagement with said rotary drive element and said passage.

15. The double disc grinder of claim 14 wherein said I arm means further includes a pivot housing supported arm means includes a pivot housing extending from said pivotal support and further includes an upper arm assembly rotatably supporting said workholders, and also including means mounting said upper arm assembly at an angle to said pivot housing.

10. The double disc grinder of claim 7 wherein said means mounting said upper arm assembly includes a detachable connection therebetween.

11. The double disc grinder of claim 1 wherein said means rotating said workholder means includes a rotary drive system carried and enclosed by said arm means.

12. The double disc grinder of claim 11 wherein said arm means includes an arm member and wherein rotary drive includes a central hub rotatably mounted on said arm member and extending therethrough and further includes a rotary drive member fixed to said central hub and enclosed by said arm member.

13. The double disc grinder of claim 12 wherein said rotary drive system further includes a drive element drivingly engaged with said rotary drive member and having portions thereof enclosed in a passage extending along the length of said arm member.

14. The double disc grinder of claim 13 wherein said drive element comprises a flexible drive element circulated through a closed path comprised in part by enfor pivotal movement and also including a connection between said pivot housing and said arm member such that said arm member extends at an angle thereto, and wherein said rotary drive system further includes a rotary motor means carried by said arm member remote from said central hub and wherein said flexible drive element is circulated through said path by a driving engagement with said rotary drive means.

16. The double disc grinder of claim 1 further including work ejector means operable to force said workpieces from each of said workholders after grinding of said workpieces has been completed.

17. The double disc grinder of claim 16 wherein said ejector means is located within said arm means centrally of said at least two workholder means. I

18. The double disc grinder of claim 17 wherein said arm means includes an arm member and wherein said means rotating said workholder means includes a central hub extending through said arm member and rotatable thereon and wherein said workholder ejector means includes ejector plunger means carried by said central hub and slidably mounted in a radial bore formed therein and also includes operating rod means carried by said arm member selectively reciprocated to contact said ejector plunger means and cause slidable movement thereof in said bore, and further includes knockout means operated by said ejector plunger engaging workpieces held in said workholder means in response to said sliding movement thereof.

19. The double disc grinder of claim 18 wherein at least one of said operating rod or ejector plunger has a radiused end portion at the contact area therebetween along an arc concentric to said central hub axis, whereby the effect of angular misalignment therebetween is minimized.

20. The double disc grinder of claim 18 wherein said means for rotating said workholders further includes a rotary drive member affixed to said central hub, and wherein said operating rod and ejector plunger are contoured to straddle said rotary drive member when in contact with each other. 

1. A double disc grinder of the type having a pair of opposing radial face grinding discs defining a pair of grinding planes and adapted to be rotated and advanced towards each other to carry out grinding of workpieces disposed therebetween, the improvement comprising: at least two workholder means, each adapted to hold a workpiece such that a single planar surface of said workpiece can be ground; arm means rotatably supporting one of said at least two workholder means on either side of said arm means; means rotating said at least two workholder means on said arm means during grinding of said workpieces; means positioning said arm means between said grinding discs so that each of said workpieces held and rotated by said workholder means remain in continuous contact with only one of said grinding discs during said rotation of said workholders and grinding by said grinding discs.
 2. The double disc grinder according to claim 1 wherein said workholder means includes a three-point support adapted to engage the workpiece on the side of said workpiece opposite to the surface ground so as to locate the workpiece surface to be ground in the planE of grinding.
 3. The double disc grinder of claim 2 wherein said workholder means includes a series of locator points extending about the periphery of said work-piece to position said workpiece laterally during grinding.
 4. The double disc grinder of claim 3 further including a member resiliently biased into engagement with said workpiece periphery exerting a retention pressure thereon.
 5. The double disc grinder according to claim 1 wherein said means positioning said arm means includes means pivotally supporting said arm means for movement between said discs.
 6. The double disc grinder of claim 5 wherein said arm means includes a pivot housing extending from said pivotal support and further includes an upper arm assembly rotatably supporting said workholders, and also including means mounting said upper arm assembly at an angle to said pivot housing.
 7. The double disc grinder of claim 6 wherein said means mounting said upper arm assembly includes a detachable connection therebetween.
 8. The double disc grinder of claim 3 wherein said means positioning said arm means includes means pivotally supporting said arm means for movement between said discs.
 9. The double disc grinder of claim 8 wherein said arm means includes a pivot housing extending from said pivotal support and further includes an upper arm assembly rotatably supporting said workholders, and also including means mounting said upper arm assembly at an angle to said pivot housing.
 10. The double disc grinder of claim 7 wherein said means mounting said upper arm assembly includes a detachable connection therebetween.
 11. The double disc grinder of claim 1 wherein said means rotating said workholder means includes a rotary drive system carried and enclosed by said arm means.
 12. The double disc grinder of claim 11 wherein said arm means includes an arm member and wherein rotary drive includes a central hub rotatably mounted on said arm member and extending therethrough and further includes a rotary drive member fixed to said central hub and enclosed by said arm member.
 13. The double disc grinder of claim 12 wherein said rotary drive system further includes a drive element drivingly engaged with said rotary drive member and having portions thereof enclosed in a passage extending along the length of said arm member.
 14. The double disc grinder of claim 13 wherein said drive element comprises a flexible drive element circulated through a closed path comprised in part by engagement with said rotary drive element and said passage.
 15. The double disc grinder of claim 14 wherein said arm means further includes a pivot housing supported for pivotal movement and also including a connection between said pivot housing and said arm member such that said arm member extends at an angle thereto, and wherein said rotary drive system further includes a rotary motor means carried by said arm member remote from said central hub and wherein said flexible drive element is circulated through said path by a driving engagement with said rotary drive means.
 16. The double disc grinder of claim 1 further including work ejector means operable to force said workpieces from each of said workholders after grinding of said workpieces has been completed.
 17. The double disc grinder of claim 16 wherein said ejector means is located within said arm means centrally of said at least two workholder means.
 18. The double disc grinder of claim 17 wherein said arm means includes an arm member and wherein said means rotating said workholder means includes a central hub extending through said arm member and rotatable thereon and wherein said workholder ejector means includes ejector plunger means carried by said central hub and slidably mounted in a radial bore formed therein and also includes operating rod means carried by said arm member selectively reciprocated to contact said ejector plunger means and cause slidable movement thereof in said bore, and further includes knockout means operated by said ejeCtor plunger engaging workpieces held in said workholder means in response to said sliding movement thereof.
 19. The double disc grinder of claim 18 wherein at least one of said operating rod or ejector plunger has a radiused end portion at the contact area therebetween along an arc concentric to said central hub axis, whereby the effect of angular misalignment therebetween is minimized.
 20. The double disc grinder of claim 18 wherein said means for rotating said workholders further includes a rotary drive member affixed to said central hub, and wherein said operating rod and ejector plunger are contoured to straddle said rotary drive member when in contact with each other. 